Diffusion apparatus



April 13, 1954 Filed Jan. 4,'1952 H. A. SAROFF ETAL DIFFUSION APPARATUS 4 Sheets-Smet 1 g] mma/low Harllyarofil 6590139 HLillard April 13, 1954 Filed Jan. 4, 1952 H. A. SAROFF ET AL DIFFUSION APPARATUS 4 Sheets-Sheet 2 Mmmm]WIJ] gru/umm GeofgeHLDilZaJ'cl April 13, 1954 Y H. A. sARoFF ET AL 2,675,349

DIFFUSION APPARATUS Filed Jan. 4', 1952 4 sheets-sheerb s HanyAa/roff K4 Genga HL. Dil Lag-d April 13, 1954 H. A. sARoFF ETAL 2,675,349

j l DIFFUSION APPARATUS Filed Jan. 4. 1952 4 sheets-snee: 4

17 Hang/A.Saroff QL GeozyeHLlla/zd Patented Apr. 13, 1954 UNITED STATES PATENT OFFICE DIFFUSION APPARATUS Harry A. Sarol, Bethesda, and George H. L. Dillard, Rockville, Md.

Application January 4, 1952, Serial No. 264,894

continuous dialysis of large amounts of solutions, has been very expensive and relatively inefficient due to limitations imposed upon the design of the equipment by the properties of available dialyzing membranes.

The foregoing objections have been overcome by this invention which comprises a membrane diffusion unit apparatus; and, in its preferred embodiment, a membrane diffusion column composed of a plurality of membrane diffusion units which are applicable to the continuous separation of dissolved molecules by means of their differ-` ences in diffusion rates. The membrane diffusion apparatus of this invention comprises, basically, a dialyzing membrane supported at an acute angle with respect to the horizontal with one end of the membrane thus elevated above the other end thereof. The dialyzing membrane is supported in this position in a manner such that it is wholly iiat or plane. The solution to be subjected to dialysis is allowed to drip upon the upper surface of the membrane at the elevated end thereof and flow by gravity thereover to the lowermost end of the membrane. The solution, when thus applied to the upper surface of the dialyzing membrane, spreads transversely across the upper surface of the membrane and flows in a fairly uniform thin film of liquid having a thickness of the order of about 0.1 mm., toward the lower end of the membrane. This film of liquid has been found to be composed of an extremely thin film or region of liquid adja- 8 Claims. (Cl. 210-8-5) cent the dialyzing membrane which moves at a Y surface of the membrane and the thin nlm thereupon wherein there is laminar flow.

The wash liquid is applied to the lower face of the dialyzing membrane at the elevated end thereof and allowed to ow by gravity to the lower end of the membrane. The flow char.

acteristics of this liquid film are substantially the same as those of the film of liquid flowing over the upper surface of the membrane. Thus, the fiowing film of wash solution includes a thin film adjacent the membrane which moves at a slow speed with laminar flow while the balance of liquid ows thereover at a greater vspeed with turbulence. At the lower end of the dialyzing membrane means are provided at the upper surface thereof to withdraw the solution which has been dialyzed and means are also provided adjacent the lower surface of the membrane to withdraw the wash liquid. The solution which has been subjected to dialysis may, if' desired, be introduced into a second membrane diffusion unit and again subjected to dialysis. A multiple surface system may be achieved merely by using a plurality of these units in series. The above membrane diffusion unit is operated under conditions where either only the smaller molecules in the solution subjected to dialysis have time to diffuse in relatively large amounts or the membrane becomes a barrier to the large molecules in solution. Either the above unit or a column composed of a plurality of these unitsybecomes a continuous dialyzer.

It is, therefore, the principal object of this invention to provide a diffusion apparatus whereinr a liquid containing dissolved molecules is permitted to iiow by gravity in a thin lm over the upper surface of a plane incline-d dialyzing membrane and a wash liquid is permitted to flow by gravity in a thin film over the lower surface of the membrane.

j Another object of this invention is to provide a diffusion apparatus employing a plane inclined dialyzing membrane, a means at the uppermost end of the membrane for depositing a solution to be processed upon the upper surface thereof,

. and a means for depositing a wash liquid to the lower surface of the membrane at the uppermost end thereof, each of said liquids thereafter being permitted to flow over the respective surfaces of the membrane by means of gravity to the lowermost end thereof.

Another object of this invention is to provide a diffusion apparatus having a plane inclined dialyzing membrane wherein liquids may flow by gravity over the upper and lower surfaces thereof as films, each of which films is composed of a thin film adjacent the surface of the membrane which moves at a slow speed with laminar flow while the remainder of the liquid in the film ows at a greater speed with turbulence.

A further object of this invention is to pro.-

vide a diffusion column for continuous separation of dissolved molecules having a plurality of plane inclined dialyzing membranes supported therein and having means for depositing liquids upon and removing liquids from the upper and 5 lower surfaces of the membranes Still another object of this invention is to provide a diffusion column for continuous separation of dissolved molecules comprising a spaced'. pair of vertically disposed frames, each having lc a plurality of horizontally disposed supportingr Y members mounted therein, the supporting members in one of the frames being staggered withrespect to those in the other frame, a dialyzing membrane extending over the supporting memle bers between the frames to provide a verticallyW extending zigzag membrane, means for depositl ing liquids to the upper and lower surfaces of the membrane and means forwithdrawing liquids' from the upper and lower surfaces thereof. 2Q

it is also an objectof this invention to provide a diffusion column for` continuous separation ofi. dissolved molecules which is compact and .in- 4 expensive to construct, and whiclfroperatesA eme, ciently. 2:

The .above and other objects of this, inventionf.- will be Aapparent from the following detaiied descript-ion and the accompanying drawings where-H in:

Figure Vl Vis a perspective view of a membrane geo diffusion unit apparatus` which embodies .than basic novel features of this invention;

Figure 2 is an end view in cross section talqenalong line 2 2 of Figure l; i

Figure 3 is a side elevational viewin cross sec.- i tiontaken along line i-of Figure 2;

Figure 4 is a side elevational view of a diffusion column comprising thepreferred embodiment of;` this invention showing theI column enclosed in a` moisture-proof cover;

Figure 5 is a top plan view ofthe column shown inFigure 4;

Figure 6 is a side elevational view of the diffusion column shown in Figure i with the moisture-v proof cover removed;

Figure 7 is an enlargedend.elevational view, partly in cross section taken along line .lei of Figure 6 and broken to conserve space, showing a portion ofthe diffusion column adjacent the topV thereof; r

Figure 8 isv an enlarged fragmentary view in d cross section taken along liney 3 8 of Figure .7 showing thetop plane inclined dialyzing memn brane in the diffusion column and themeans for depositingliquids to the surfaces thereof;

Figure e :is an enlarged fragmentary top view in cross section taken along line 9 9 .of Figure 6 showing the means for mounting a membrane support in the frame of the diffusion column;

Figure 1G is an enlarged fragmentary end view in cross. section showing a combined membrane support and means for removing liquid from a surface of the membrane; and, as well, the flowing films of solution upon the surfaces of the membrane;

Figure 11 is a fragmentary broken perspective view showing the combined membrane support and means for removing liquid from theA membrane which is 'shown in Figure 1G; Y

Figure 12 is an enlarged fragmentary end view 70 of a portion of a membrane and a support there" f for showing the nlms of liquid owing on theupper and lower surfaces thereof;

Figure 13 is an enlarged fragmentary ViewY partly in cross section of va manifold for deposit- 75 ing liquid upon a surface of the dialyzing membrane;

Figure 14 is an enlarged fragmentary view partly in cross section showing modified forms of manifolds for depositing liquids upon the upper and lower surfaces of a dialyzing membrane;

Figure 15 is an enlarged fragmentary View in cross section showing the modied form of manifold shown in Figure 14;

Figure 16 is an enlarged broken fragmentary top plan View of a modified form of a combined membrane support and means for removing the liquid from-a surface of the membrane;and

Figure 17 is an enlarged end view in cross section taken along line Il il of Figure 16 of the be formed of a transparent synthetic resinous maferial is composed of upper and lower sections 3 and il respectively. A dialyzing membrane is positioned between the abutting faces of the upper lower sections S and/2 of the. chamber i and is sec red therebetweencin-.a manner such that the membrane is free of Ywrinkles andis come..v pletely flat throughout the. entire extent thereof.

The dialyzing membrane is thus vprovided with upper and lower surfaces `and i, respectively,

which are plane surfaces. All four edges of theL mbrane Si -be placedunder tension inthis lorrn ofthe invention and any tendency thereof to sag is thus eliminated.k

The chamber l is tilted or inclined with respect to the horizontal asis shown in Figure 3,

position of the chamber is, however, not im-v portant, it only being essential that the dialyzing membrane 5 supported therein be inclined at anV acute angle with respectrto the horizontal.4 rlhe angle of inclination disclosed in Figure 3 `is Aapproximately 10 but this may be varied depend-VV ing upon factors which willbe discussed hereinbelow.

The elevated end 3 of the upper section 3 of* the chamber l is provided with an opening through which a fiuid conduit 9 may extend. The outer end of the conduit 9 is connected to a fluid ysupply pipe IG which is lconnected to a reservoir of a liquid to be subjected to dialysis. The inner,V endcf the conduit 9 is connectedto a manifold i i which is provided with a plurality of fluid out. lets i2 positioned immediately above the upper surface of the membrane 5 at the elevated end thereof.V rEhe elevated end it, .of the lower section :lof thel chamber is similarly provided wit an opening adapted to receive a liquid conduit it which is attached to a uid supply pipe Vi5 that is Yconnected to a supply of wash water. The inner end of the conduit i4 isconnected to a manifold l5 Awhich isl provided with a plurality of uid outlets il. These outlets are positioned immediately below Ythe lower surface of the membrane 5 at the elevated end thereof.

The lower end i5 ofthe upper section 3 of the chamber I is provided with an opening adjacent the upper .surfacevof 4the .membrane 5 which opening is adapted to receive a conduit-lt. The conduitle is connected to an outlet pipev 253i' whichmaywlead` to a collecting receptacle.which..

is not shown or to the conduit 9 of an adjacent membrane diffusion unit, if several such units are employed in series. The lower end 2l is provided with an opening which is adapted to receive a conduit 22 that is connected to an outlet pipe 23. The latter may be connected to a drain or other means for disposing of the used wash water.

The dialyzing membrane 5 employed in the diusion unit shown :in Figures l to 3 may be formed of any of the materials commonly used for dialyzing purposes. The membrane may be formed of fibrous or non-fibrous wettable materials as a class. The non-fibrous materials include films of such materials, as for example, cellulose hydrate, alkali-soluble cellulose ethers, cellulose esters, mixed ester-ethers of cellulose, gelatin, casein, permeable and semi-permeable resins, porous glass and the like. The cellulose ethers may comprise the alkyl ethers, the hydroxy-alkyl ethers, the carboxy-alkyl ethers, and the mixed ethers such as alkyl hydroxyalkyl cellulose ethers and the cellulose ether Xanthates. The cellulose esters which may be used include lms formed of low nitrated cellulose nitrate, low esteried cellulose acetate and cellulose formate. The cellulose hydrate may be regenerated from viscose or from cupraammonium solutions of cellulose. Among the film of solvent swelling resins which may be used are those formed from permeable and semi-permeable polymers of acrylic acid, methyl methacrylate and polyvinyl alcohol resins in the A stage. Wettable fibrous materials include parchment paper, glass fiber cloth and the like. It is pre ferred to employ films of cellulose hydrate; such as, for example DuPont 600PT having a thickness of 0.0016 when dry or Visking sausage casing having a thickness of 0.00155 when dry.

The dialyzing membrance 5 is moistened and care taken to prevent any deposition of oil or grease upon the surfaces thereof. The membrane is then stretched, levelled and secured between the sections of chamber I. The liquid to be subjected to dialysis is then deposited through the outlets I2 by gravity only upon the upper surface 6 of the membrane 5 at the elevated end thereof. The liquid spreads laterally over the upper surface 6 and flows thereover toward the lower end of the membrane 5 by gravity as a thin film having a thickness of the order of 0.1 mm. This film of fiowing liquid is composed of a thin film adjacent the surface 6 of the membrane which moves at slow speed. The character of the flow in this thin nlm is laminar. i The remainder of the flowing liquid thereabove moves with greater speed in a turbulent manner. In the turbulent portion of the flowing film of liquid the solution circulates in a direction normal to the membrane 5 with the result that there is no concentration gradient of the larger molecules adjacent the portion of the film owing in a laminar manner.

The wash water is deposited upon the lower face I of the membrane 5 at the upper end thereof by the outlets Il. The wash water spreads over the surface of the membrane 5 and flows, by gravity, toward the lower end of the membrane as a thin film. This film is composed of a portion adjacent the membrane 5 which flows at slow speed in a laminar manner while the remainder of the film moves with greater speed in a turbulent manner. As the films flow over the upper and lower surfaces 6 and 1 of the membrane,.the molecules having the greatest rate of diffusion migrate through the laminar flowing portion of the film adjacent the upper surface 6 and the membrane 5 into the thin film of wash water flowing over the lower surface of the membrane. When the nlm of liquid owing over the upper surface E of membrane reaches the lower end thereof it is removed therefrom through the conduit I9 and the outlet pipe 20. The wash water flowing on the lower surface 1 of the membrane ows over the inner surface of the lower end 2| of the section 4 of the chamber and is withdrawn therefrom through the conduit 22 and the outlet pipe 23.

In one experiment with the diffusion unit described above a solution of 0.1M sodium chloride was permitted to flow at a rate of 5 ml. per minute over the upper surface 6 of a membrane 5 having an area of 5,0 square inches. Wash water was permitted to flow over the lower surface 1 of the membrane at the rate of 150 ml. per minute. Under these conditions 30 percent of the salt was removed in a single traverse.

The basic principles of the diffusion apparatus of this invention have been utilized in a compactly arranged diffusion column adapted for use in continuous dialysis of large amounts of solutions as well as in the simplied diffusion unit shown in Figures l to 3. The diffusion column shown in Figure 4 is mounted in a collecting basin 24 which rests upon a support 25. The diffusion column is enclosed in a moisture-proof cover 26 provided with window 2l' which permits observation of the column when it is in operation. The cover 25 is employed for the purpose of providing a chamber for the diffusion column in order that the air therein may be kept saturated with moisture. The operation of the diffusion column is enhanced by maintaining the air therearound saturated with liquid. The diffusion column is more clearly shown in Figure 6 with the moisture-proof cover 26 raised to the top of the column. The diffusion column is composed of a pair of spaced frames indicated generally as 28 and 20 each of which frames consist of two upwardly extending square hollow posts 30 which, of course, may have any other desired shape. The lower-most ends of' each post 30 in each of the frames 2S and 20 are connected by plate members 3i, and the lower ends of the posts 30 and the plates 3l of the frame 29 may be welded as shown or otherwise secured to the collecting basin 24. The frame 28 is, therefore, free to be moved toward or away from the frame 2S. The frame 2S may also be f'urther supported by the angularly disposed bars 32 which may be secured at one end to the frame as shown in Figure 6 and welded, at the other end thereof, to the collecting basin 24. The opposed posts 3G in each of the frames 28 and 29 are provided with apertures which are aligned to receive tensioning rods 33. The tensioning rods 33 thus extend through aligned apertures in opposed posts 30 and are positioned horizontally. The rods 33 are provided with threads 34 at one end which are adapted to receive nuts 35 and 3S with washers which engage opposite faces of the posts 36 in the right-hand frame `20. The rods 33 are thus firmly secured to the posts til in the right-hand frame 29 and no relative movement between the posts and the rods may occur. The opposite ends of the rods 33 are provided with threads 3l which extend a substantial distance along the length of the rod. In assembling the frames 28 and 29 a nut 38 and washer 39 may be placed upon each of the rods 33 before the ends of latter are inserted in the apertures provided in the left-hand `frame 28. At the same time two coiled springs 40 adapted to receive the outlet pipes` Ell. The manifold 55 is provided with about fifteen such outlets spaced about an inch apart. The outlet pipes may be secured in the manifold 55 by the lock nuts Sl shown in Figure 13. The ends of the outlet pipes Bil are threaded to receive interchangeable cannulae '62 which permits the use of cannulae of different sizes. Interchangeable cannulae, in conjunction with diiferent heads of fluid in` the reservoir 5i makes it possible to vary the rate of now of the liquid to be subjected to dialysis within desired limits. The position of the manifold 55 and the distance of the outlet pipes Gt from the surface of the membrane lill may be varied by loosening the screw 58 and mov ing the bracket 55. The bracket 58 may also be rotated to vary the angle of the interchangeable cannulae 62 with respect to the surface of the membrane 50.

The wash water employed in the diffusion colf umn of this invention is supplied at a constant head from a reservoir 53 mounted upon the top 43 of the diffusion column. The reservoir 63 is supplied by a pipe 64 and is provided with an overflow pipe 55. A. plurality of conduits 66 are connected to the bottom of the reservoir 63 to feed wash water therefrom. The conduits 66 pass through apertures provided in the top I43 into the diffusion column and are each connected to a. manifold 55a. One of the manifolds 55a is supported immediately beneath the lower surface of the membrane 5l) adjacent the terminal end thereof secured to the uppermost membrane support il@ in the left-hand frame 28. This manifold is supported by rotatable and sliding brackets etc which are locked by screws 58a to lugs 59a mounted on the outer faces of the posts 3l! of the left-hand frame 2B. The screws 53d extend through slots 51a provided in the brackets 5ta and these may be loosened to permit adjustment of the position of the manifold 55a with respect to the surface of the membrane- 50. It is usually desirable to deposit fresh wash water upon the membrane 50 at several points along the length thereof. additional manifolds 55a at different points in the diffusion column to either the left or right-hand frames 28 and 29. In Figure 6 the right-hand frame 29 is shown with two such manifolds 55af supported by brackets 58a which are secured to ,g

The additional manifolds 55a are always positioned adjacent a combined membrane support and liquid stripping tube 45 as is shown in detail in Figure 10.

The means for removing a liquid from a suiface of the membrane comprises a tube 45 having a slot 6T formed in the sidewall thereof as is shown in Figure 11. These liquid stripping. or removing tubes 45 are supported in either the frame 28 or 29 in a journal of the type shown in Figure 9. A tube 45 is employed adjacent each of the manifolds 55a for the purpose of withdrawing the wash liquid flowing, at that point, over the lower face of the membrane 59. The position of the edge of the slot el adjacent the surface of the membrane 5u from which the flowing film of liquid is to be removed is an important feature of this invention. This edge of the slot (il is spaced from and positioned below the lower surface of the membrane 5G over which the film of liquidto be removed is nowing as is shown- This may be accomplished by supporting lll in Figure 10. It has been discovered. that, when this relationship between surface of the membrane and the edge of the slot is maintained, there is no mingling of the ilowing films of liquids on the upper and lower surfaces of the membrane 5t around the edges of the latter at the bends of the dialyzing membrane formed by the membrane supports. The flowing illm of liquid passes over the edge of the slot 61 and into the tube 5. The liquid then passes from the tube l5 through one or more conduits 68 yhich may lead t0 the collecting basin at the base of the diiusion column. A tube l5 is also employed as the lowermost membrane support in the left-hand frame 28. Thus tube 45 collects the liquid which has been subjected to dialysis from the lower surface of the membrane 5t and the liquid collected is led by a conduit 69 to al collecting receptacle which is not shown.

A modied form of liquid collecting tube is shown in Figures 16 and 17 of the drawings. The modified form of tube 45d is provided with an opening 61a in the sidewall thereof and the edge of the opening which is positioned adjacent the lower surface of the membrane Eli over which the nlm of liquid to be removed is flowing is provided with an extension which is curved inwardly within the tube 45a. This curved extension of the edge of the opening Sie is shaped in the form of a modified helix.

A modified form of manifold for `depositing liquid upon the surfaces of the membrane 5t is shown in Figures 14 and 15. The manifold'lll provided with a plurality of liquid outlets arranged along the top thereof. The liquid nowing from the manifold through the openings provided therein flows downwardly over both sides of the manifold. A distributor bar 'H is attached to the bottom of the manifold 'l0 by the bands l2. The bar ll, which may be formed of a plastic material, is positioned very close to the upper surface of the membrane 5i), preferably about 0.01 mm. therefrom. The liquid flowing over the sides of the manifold lil has become distributed to a certain extent and the bar 'll serves to complete this operation with the result that the liquid is deposited on the surface of the membrane 5u across the entire width thereof immediately. This modified form of manifold is not adapted for depositing a liquid to a lower surface of the membrane 5t; and, in order to deposit a liquid upon such a surface, ij; is necessary to `position the manifold 'lil in advance of a membrane support above the bend formed thereby in the membrane. The arrangement of the manifolds adj acent the uppermost end of the left-hand frame 23 shown in Figure 5 may be modified as is shown in Figure 14. In this modied arrangement, employing the manifolds 'It foi` depositing the wash liquid, the portion of the membrane 5t in advance of the upper manifold 'Hl may be anchored to the diffusion column in any desired manner. A particular advantage of the arrangement shown in Figurell resides in the fact that the portion of the membrane 5l! extending from beneath the membrane support is thoroughly wetted before the liquid to be subjected to dialysis is deposited upon the upper surface thereof with the result that no wrinkling of the membrane takes place at this point.

In operating the diffusion column ycomprising this invention the desired rate of flow of the liquid to be processed from the manifold is determined. The rate of flow may be controlled by employing cannulae in themanifold having an This, in turn, determines the amount of turbulencel which will be produced in vthefree flowing fllms'of liquid. "Theidesired angle of the membrane'sections may be obtained @by employing frames 28 and 29 wherein the vertical displacement of the/membrane .supports in one frame'With-respeot to the vertical position ofthose vin the other frame is suchthatthedelsired angle of the lmembrane lsections With rel spect tothe horizontal is provided. 'The' 'diffusion column' -is then assembled: andV the-@dialyzmg membrane 5t yarranged thereininthe vertically extending-sinuous manner described. 'The solution to beprocessed isintroduced ntothefreser- -fvoir' 5i andthe Awash liquid. is supplied toithe Mreservoir. The liquid toi be :processed ows -from'the ycannulae iii! in .the manifold 55u-and is v`deposited uponthe upper surface of the firs'tiinclinedsection fof the` membrane-53. "iSirnul- .'taneously the Wash'liquid is deposited uponthe lower surface of the membrane 5G adjacent'the `upperend ofthe 'frame Z8. The liquids deposited upon the upper andlowersurfaces of themem- "fbrane'BU move as free l'owinglillms toward the uppermost membrane support in 'the' right-hand `frame"2l. Each of these -free iiow ilmsfis com- 'posed-"oi aflaminarbiiowing portion adjaeent'the membranefandan outerturbulently nou/ing por- Stion. 'When the upper*andlowerowingklms v reach'the `first bend provided' bythe uppermost support` in the' frame 29the liquids floivioverthe -outside'l and around thelins'idec'of 'the bend as is "shown'finligure i12. Theliquids remain on` their respective surfaces of the membrane 59 and do 1 not flow over tl 1e edges thereof: nor otherwise -mingle At any numberfof desired'points inthe diiusion column adjacent eitherl oiixthe frames '2E or 29 the wash liduidimay .be removed'by'employing a tube #i5 or! ea as amembranesupport andiy fresh wash liquiddepositedA onythe'membrane as .is shown in Figure l0.' The wash'liduid may be lcollected if itis desiredrto recover a solu- 4tion of the'molecules whichLdiffuse'through the membrane eil. The liquid which hasbeen' processed mayalso be :removed by employing; a tube 45 ori 15a as a membrane support. as isfshown-:at

v'the lower ofthe vleft-handt frame` 281-in Figjure 6. Thelatter liquid '.mayalso `be collected and recovered. :If desired, :the Wash Yliquid'rremoved iromthe column adiacentfthe-lower portion Vthereof may bel redepositedruponxthemembranefat a point in 'fthe upper portion of the; dif- 'ffusion column. This, :is permissible-because'foi the lovv concentration; oft'diffusedglimolecnlese in v[the wash liquid removed from-...theflower-portion *of the diffusion column.

"The selection of therate ofilowofxtheliquid to be processed in operating eitherythediiusion Vvunit shown 'in'FiguresL lfto. 3 'or thediffusion l2 v lrecoveredrin. they lprocessed liquid increases. f- As "theirate of'iiow is increasedit-.has' been: ascerftained that-the ratio of the percentage oflarge a Vmolecules removed-'from the' liquid being` proc- D Aesseci to the percentage vofsmall moleculesfrecolumnl described above must be made with the Y V'ieWfto obtaining maximum efficiency. The rate of flow ofthe Wash liquidis not'especially critical large molecules 'in solution -therein vwhich are "-movedvtherefrom decreases. Therefore, the' :ef- 1' ciency oisepar'ation diminishes if the ratefoi ffflowfoflthe liquid being processed is increased. Itfiiiillv beapparent that optimum results will -be 'obtained for any given solution 'of large' and smalll molecules if a rate 'of'ilow rthereofisrem ployed at 'which'maximumfelciency of separation Yis obtained; and, as well, as high afpercentage-of large molecules as possible'fin the:=liquid 5 processed is recovered. vV'Ihis. relationship :was demonstrated' ina fdiiusion' column havingv a v'membranesupported'therein of an areafof v'1090 -fsquare inches Aemploying'a 1 to 1v molar'ratio solution of sugar and salt. Three wash vjetsvvere @employed-'Which'supplied Water at a ratelofow ofl'i) mI./min."lThe' following rates of iloW-of fthey 'ab-ove solution fgave the results' indicated:

Ratio ci 9 Sucrose Salt Re- 'f Percent Removed moved. Sucrose Rateof Flow, nil/min. From From Removed Solution, Solution, `toPercent -xPercent vPercent ...S t

` YRemoved 5s 95 0.61 w44 89 z 0.49 30 ..77 ``0.?,9 23 es 0. 37 20 A 00 0. 33 .117 .52 0.33

#The/features of this-invention: may, obviously;Y be embodied in formsof :equipment not specifically Urfdis'closed herein. Such. otherfequipmenttmay. be

devised readily by persons'skilledzin this art and iQ-to Whom thev fundamental.principles;heren;.dis

'closedi are made. available. Many: forms; of vap- --paratusl may be constructed wherein. ai. dialyzing membrane is supported toprovide lat;fplane'sur *faces and' means are provided `whereby aliouid rcontaining)dissolved molecules and a `wash liquid may-be vdeposited'on'opposite'surfaces of the membrane and passed thereover in vthe Vforni l of thin freely -lowinglms All equipment capable "ofY carrying outdiffusion processes-in the-'man "J ner describedis intended tofall Withinthe scope of `the appendedclairns.

' We claim: 1.- A` diiusion vcolumncomprising a'spaced pair :'of upwardlyv `extending supporting members, a

5' plurality of horizontally disposed membrane' supporting members mountedl on each of said supporting` members,k the membrane i supporting members in one of said supporting-members being* vertically-displaced with respect to the ad- 'jacent opposite'membrane supporting members in' the; othersupporting member a dialyaing .mernbranerm'ounted upon the membrane supports of eachv of said supporting members,V said membrane 'extending transversely of said difiu- Vsion column alternately between adjacent opposite membrane supporting members throughout said .column whereby saidmernbrane occupies a vertically disposed sinuouspath, means for' depositirig` aliquidlcontaining dissolved molecules on one of the surfaces of said membrane adja- .centtheuppermostend thereof, means for depositing a wash liquidV to the other surface of vsaid membraner adjacent the uppermost end thereof', meansvfor removing thefliq'uid 'contain- -ingidissolvedmolecules'iromfthe surface of said membrane mounted on one of said supporting members, and means for removing Wash liquid from the other surface of said membrane mounted on one of said supporting members.

2. A diffusion apparatus as set forth in claim 1 characterized in that the means for depositing liquid upon a surface of the membrane comprises a manifold provided with liquid outlets in the top thereof, a fluid distributing bar mounted on the bottom of said manifold and means for securing said distributor bar to said manifold.

3. A diffusion column as set forth in claim 1 characterized in that said upwardly extending supporting members comprise a spaced pair of vertically disposed frames, a supporting means immovably secured to one of said frames, and a supporting means for the other of said frames, said last named frame being laterally moveable toward and away from the other of said frames whereby the tension upon the sinuously disposed dialyzing membrane, supported by said frames may be varied.

4. A diffusion column as set forth in claim 3 characterized in that said second named supporting means comprises at least one member mounted on each of the adjacent opposed sides of said frames and extends transversely therebetween, each of said members being immovably secured to one of said frames and movable with respect to the other of said frames, and means mounted on each of said transversely extending members for exerting pressure between said frames to cause one of said frames to move away from the other of said frames whereby tension may be placed on the sinuously disposed dialyzing membrane supported by said frames.

5. A diffusion column as set forth in claim 1 characterized in that a plurality of journal members are mounted on each of said upwardly extendingr supporting members. each of said membrane supporting members being mounted in said journal members whereby said membrane supporting members may rotate when tension is applied to the dialyzing membrane supported thereupon.

6. A diffusion column as set forth in claim 5 characterized in that the membrane supporting member at the top of one of said supporting members and the membrane supporting member at the bottom of one of said supporting members are each provided with means for rotating said members, and locking means mounted on said upwardly extending supporting members adjacent each of said membrane supporting member rotating means for locking said membrane support members to prevent rotation thereof.

7. A diffusion column as set forth in claim l characterized in that each of said upwardly extending supporting members is provided with at least one dialyzing membrane support comprising a tube having a horizontally disposed elongated opening in the sidewall thereof for removing liquid from the lower surface of the membrane supported thereon, the edge of said opening adjacent the surface of the membrane from which the liquid is to be removed being spaced from and positioned below said surface of said membrane.

8. A diffusion column as set forth in claim 7 characterized in that the edge of the opening in said tube adjacent the surface of the membrane from which the liquid is to be removed is provided With an extension in form of a modified helix which extends within said tube.

References Cited in the file of this patent UNITED STATES PATENTS Number 

1. A DIFFUSION COLUMN COMPRISING A SPACED PAIR OF UPWARDLY EXTENDING SUPPORTING MEMBERS, A PLURALITY OF HORIZONTALLY DISPOSED MEMBRANE SUPPORTING MEMBERS MOUNTED ON EACH OF SAID SUPPORTING MEMBERS, THE MEMBRANE SUPPORTING MEMBERS IN ONE OF SAID SUPPORTING MEMBERS BEING VERTICALLY DISPLACED WITH RESPECT TO THE ADJACENT OPPOSITE MEMBRANE SUPPORTING MEMBERS IN THE OTHER SUPPORTING MEMBER, A DIALYZING MEMBRANE MOUNTED UPON THE MEMBRANE SUPPORTS OF EACH OF SAID SUPPORTING MEMBERS, SAID MEMBRANE EXTENDING TRANSVERSELY OF SAID DIFFUSION COLUMN ALTERNATELY BETWEEN ADJACENT OPPOSITE MEMBRANE SUPPORTING MEMBERS THROUGHOUT SAID COLUMN WHEREBY SAID MEMBRANE OCCUPIES A VERTICALLY DISPOSED SINUOUS PATH, MEANS FOR DEPOSITING A LIQUID CONTAINING DISSOLVED MOLECULES ON ONE OF THE SURFACES OF SAID MEMBRANE ADJACENT THE UPPERMOST END THEREOF, MEANS FOR DEPOSITING A WASH LIQUID TO THE OTHER SURFACE OF SAID MEMBRANE ADJACENT THE UPPERMOST END THEREOF, MEANS FOR REMOVING THE LIQUID CONTAINING DISSOLVED MOLECULES FROM THE SURFACE OF SAID MEMBRANE MOUNTED ON ONE OF SAID SUPPORTING MEMBERS, AND MEANS FOR REMOVING WASH LIQUID FROM THE OTHER SURFACE OF SAID MEMBRANE MOUNTED ON ONE OF SAID SUPPORTING MEMBERS. 